As a multi-carrier transmission mode, Orthogonal Frequency Division Multiplexing (OFDM) reduces the sensibility of a system to multipath fading channel frequency selectivity by converting a data stream transmitted at a high rate into a group of data streams transmitted in parallel at a low rate while the introduction of cyclic prefix further improves the Inter-symbol Interference (ISI) resistance of the system. Besides, characteristics including high bandwidth efficiency and easy implementation etc. enable OFDM technology to be applied more and more widely in the radio communication field. For example, Wireless Local Area Network (WLAN) systems, 802.16e systems based on Orthogonal Frequency-Division Multiple Access (OFDMA), and the next generation 802.16m systems of 802.16e etc. are systems based on OFDM technology.
For a mobile communication system, a Mobile Station (MS) is accessed to a network usually by a Synchronization Channel (SCH), and related systems of the current system are transmitted by using preambles in the SCH according to the following steps.
1) time and frequency synchronization.
2) cell Identifier (ID) detection.
3) broadcast message reading.
Through the steps above, the MS starts subsequent access processes according to information in the broadcast message.
In the mobile communication system, the access of the MS may be divided into an initial access process and a non-initial access process, wherein the initial access refers to a process in which the MS is powered on and accessed to a system while the non-initial access process refers to an access switching process, wherein an important index of the access process is the access time. The shorter the access time is, the higher the system performance will be. However, the access process needs to be implemented by the SCH which occupies certain resources.
In the conventional art, synchronization preambles comprise one Primary-Preamble (P-Preamble) and three Secondary-Preambles (S-Preambles) respectively carried on four radio frames of a superframe, thus causing relatively large overhead of SCH during a synchronization process.